The studies proposed involve both current and proposed treatment protocols for malignant disease in children. For acute lymphocytic leukemia, the current new patient study is designed to investigate front-end immunologic parameters such as immunoglobulins, skin-testing, HLA typing and immunologic history, and relate them to disease state and outcome. The treatment program will involve a more intensive induction and intensification program for half of the children who have initial WBC's over 20,000, and/or mediastinal masses. The other half of these children will be treated in the same way as the children who have counts less than 20,000 initially and no mediastinal masses. All children will receive CNS prophylaxis with cranial irradiation and IT methotrexate. Children with acute granulocytic leukemia are receiving induction therapy with 5 drugs and maintenance therapy with monthly cycles of 4 drugs. Immunotherapy with BCG and leukemic cells is being given in 3 doses during the first 3 months of chemotherapy to half the children. Tumor studies include participation in the National Wilms' Tumor Study, Part II, Intergroup Rhabdomyosarcoma Study, and the Intergroup Ewing's Sarcoma Protocol for both new patients and patients with metastatic disease. New studies for metastatic and localized neuroblastoma and histiocytosis are being revised currently. BIBLIOGRAPHIC REFERENCES: R. Heyn, P. Joo, M. Karon, M. Nesbit, N. Shore, N. Breslow, J. Weiner, A. Reed, and D. Hammond. BCG in the treatment of acute lymphocytic leukemia. In press, Blood, September, 1975; M.E. Lahey, W. Borges, A. Evans, R. Heyn, W.A. Newton, and L.G. Thatcher. Histiocytosis X-Comparison of three treatment regimens. In press, J. of Pediatrics, 1975.